(a) Field of the Invention
This invention relates to a circuit for driving both printing devices in an electronic cash register having a journal printing device and receipt printing device.
(b) Description of the Prior Art
In a cash register, there are required a journal printing device for continuously recording sales and a receipt printing device for making receipts to be issured to buyers. These two kinds of printing devices print the same contents on journal paper and receipt paper. However, in a conventional cash register, respective driving circuits to be used for the journal printing device and receipt printing device are wired in separate systems to be operated respectively separately. This is based on the reason that the objects of using the journal printing device and receipt printing device are differnt from each other. That is to say, the journal printing device is used to make records to be preserved and, therefore, for example, the date may well be printed only at the time of the first printing every day. Therefore, in the case of the subsequent printing operation for the day, when the date is to be printed, the driving circuit should be preferably cut off. On the other hand, the receipt printing device must be operated at any time as required. Therefore, it is preferable that the driving circuit for the receipt printing device can be switched to be operative and inoperative separately from the driving circuit for the journal printing device.
FIG. 1 shows a conventional driving circuit of this kind. In the drawing, symbols J.sub.1, J.sub.2, . . . indicate journal printing driving circuits and R.sub.1, R.sub.2, . . . indicate receipt printing driving circuits. M.sub.1, M.sub.2, M.sub.3, M.sub.4, . . . indicate magnets (electromagnets) for printing respective figures. D.sub.1, D.sub.2, D.sub.3, D.sub.4, . . . indicate spark voltage absorbing diodes connected in parallel respectively with the respective magnets. Tr.sub.1, Tr.sub.2, Tr.sub.3, Tr.sub.4, . . . indicate magnet operation controlling transistors connected in series respectively with the respective magnets. In this circuit, now, if a current source is connected only to the journal printing driving circuit and the printing signals of respective required figures are given to the transistors of the corresponding figures, the magnets corresponding to them will be energized, the required types will be selected and the journal paper will be printed. In this case, the printing signals will be given as pulses and therefore a spark voltage will be generated in the magnet when de-energized but will be absorbed by the diode connected in parallel with the magnet. On the other hand, in case a receipt is required, the current source will be connected to the receipt printing driving circuit by a switch not illustrated and the same operation as the above mentioned operation of the journal printing device will be performed. Therefore, the same printing will be made on the journal paper and receipt paper and the receipt paper will be able to be issued as a receipt.
However, according to such circuit system, the same wiring circuits are provided separately and thereby there have been defects that the number of component parts (such as transistors) is large and the manufacturing cost is high. Therefore, in view of this point, such driving circuit as shown in FIG. 2 is suggested as an improvement of the above mentioned circuit system. According to this driving circuit, the circuit portion consisting of the magnet and spark voltage absorbing diode connected in parallel with it is the same as in FIG. 1 but a transistor common to both paired journal printing and receipt printing magnets is connected. That is to say, reverse current preventing diodes Da, Ab, Dc, Dd, . . . are connected in the normal direction in series respectively with the paired journal printing magnets and receipt printing magnets M.sub.1, M.sub.2, and M.sub.3, M.sub.4, and further respective transistors Tra, Trb, . . . are connected respectively between the respective connecting points of the paired diodes Da, Db and Dc, Dd and the current source. Therefore, in this case, if either or both of the journal printing driving circuit and receipt printing driving circuit are connected to the current source in advance, when a printing signal of a required figure is given, for example, when a printing signal is given to the transistor Tra for controlling the first figure printing and the transistor is made to conduct in case only the journal printing driving circuit is operative, the magnet M will operate and, in case the receipt printing driving circuit is also operative, the magnet M.sub.2 will also operate together to print the respective sheet of paper. In this case, the spark voltages will be absorbed respectively the diodes D.sub.1 and D.sub.2.
As evident from the above explanation, in the case of FIG. 2, as compared with the case of FIG. 1, there is a disadvantage that, though the number of the transistors for controlling the operation is reduced to be half, the diodes Da, Db, Dc, Dd, . . . for preventing the reverse current are newly required.